Everyday Hand Use Shapes How the Brain Processes Images

Consider hammering a nail into a wall: your dominant hand swings the hammer, while the other steadies it. In a novel theory, Cornell psychology researchers propose that common tasks like this impact how our brains process visual information – with one hemisphere specializing in high-frequency detail and the other handling low frequencies.

Research has long shown that for most people, the brain's left side responds quicker to rapidly changing inputs like hammering (high-frequency), while the right handles more static events (low-frequency) such as holding a nail. However, scientists were lacking an explanation for this phenomena.

The "action asymmetry hypothesis" by Cornell University researchers explains this and shows that high-frequency visual specialization is reversed in left-handed individuals.

"We discovered the same pattern observed in right-handers, whose left hemispheres excel at perceiving high-frequency visuals—while the opposite holds true for left-handers," said Daniel Casasanto, associate professor of psychology and director of the Experience and Cognition Lab. These findings support our theory that how the brain's perceptual systems function depends on how we perform actions with our hands.

Casasanto is senior author of "Frequency Asymmetries in Vision: The Action Asymmetry Hypothesis," published in the Journal of Experimental Psychology: General. The first author is Owen Morgan, a doctoral student in psychology.

Theories on hemispheric visual perception asymmetry have posited it might develop prenatally or be linked to language. However, the new study contradicts these theories as handedness does not reverse fetal development or the hemisphere's language processing.

Building upon Casasanto’s "body specificity hypothesis," which shows people's minds are shaped by how their bodies interact with the world, Casasanto and Morgan explored motor action's role. They repeated prior experiments to establish frequency perception asymmetry, but crucially included left-handers—previously underrepresented in research.

"Testing both righties and lefties was key to understanding how our perception is organized, and why," Casasanto said.

In experiments involving nearly 2000 participants (right-, left- and mixed-handed), they confirmed hemisphere-specific high-frequency visual processing. Reaction times were measured when "hierarchically constructed" shapes flashed on a screen.

A third experiment concluded that both righties and lefties use their left hemisphere for high-frequency sounds in language, ruling out language laterality as the reason for hemispheric differences in visual perception.

Why might right-handers and left-handers process high-frequency vision differently? The authors suggest two possibilities: once a hemisphere handles fast actions, efficient connections might form with similar motor, vision, and hearing systems. Alternatively, dominant hands may continually feed high-frequency sights and sounds into that side's visual field.

"Hand action asymmetry leads to asymmetries in visual and auditory input," Casasanto said. "The hemisphere typically processing this type of information may become specialized for it."

Low-frequency visual input did not strongly reverse, possibly because either hand performs many static tasks like holding a nail—reducing specialization.

After finding that high-frequency visual processing reverses with handedness, supporting the action asymmetry hypothesis, Casasanto plans future research on whether this applies to hearing and tests on stroke patients with lost dominant hand use. They hypothesize hand action asymmetries cause perception asymmetries in vision and audition.

"Our theory is that hand action asymmetries shape how we perceive visually and auditively," he said. "Hand actions influence several cognitive functions, including language, emotion, and—now known—visual perception."